1. The Science Program of CLAS12 and the JLab 12 GeV Upgrade
Latifa Elouadrhiri
Jefferson Lab
December 4, 2009

2. Outline Brief historical overview
Generalized Parton Distributions - a unifying framework of hadron structure
Experiments to access GPDs
12 GeV Upgrade project
3D Imaging of the Proton Quark Structure
Summary

3. Some well known facts about the proton
Charge: Qp = +1
It has a neutral partner, the neutron, Qn = 0
Mass: Mp ~ 940 MeV/c2
Proton + neutron make up 99.9% of the mass of the visible universe
Spin: s = ½ћ
Magnetic moment mp = 2.79mN
Anomalous magnetic moment ma = 1.79mN
1950’s: Does the proton have internal structure?
The exploration of the internal structure of the proton
began in the 1950’s with Hofstadter’s experiments.

4. Electron Scattering as a Probe of the Proton Structure
elastic
inclusive
exclusive
p, r, g gv gv gv
Q2 = -(e-e’)2
n = Ee – Ee’
xB = Q2/2Mn
t = -(p-p’)2
xB = 1 (for elastic scattering)
1/Q2 is spatial sensitivity of virtual g

5. Does the Proton have finite size?
Elastic electron-proton scattering
the proton is not a point-like particle, it has finite size
ds/dW = [ds/dW]n.s.|F(q)|
1955
Proton form factors, transverse charge & current densities
Physics Nobel Prize
1961 R. Hofstadter

6. What is the internal structure of the proton?
Nobel prize 1990
J. Friedman H. Kendall R. Taylor
=> Deep inelastic electron-proton
scattering
ep→e’X
ds/dWdE’ = ds/dWMott[W2 (Q2,n)]
1968
= 1/xB
Scaling => Quarks are point-like objects!
Determine quark momentum distribution f(x).
Quarks carry ~ 50% of the proton momentum.

7. ? How is the Proton Charge Density Related to its Quark
Momentum Distribution?
D. Mueller, X. Ji, A. Radyushkin, A. Belitsky, …
M. Burkardt, … Interpretation in impact parameter space
Correlated quark momentum
and helicity distributions in
transverse space - GPDs ?
Proton form factors, transverse charge & current densities
Structure functions,
quark longitudinal
momentum & helicity
distributions

8. GPDs & PDFs z z y x x x 2-D Golden Retriever 3-D Golden Retriever
Deeply Virtual Exclusive Processes & GPDs
1-D Golden Retriever
Water
probablity
Calcium
Deep Inelastic Scattering
& PDFs
Carbon x

9. 3 dimensional imaging of the nucleon
Deeply Virtual Compton Scattering (DVCS) t
x+x
x-x
hard vertices
2x – longitudinal
momentum transfer
x – longitudinal quark
momentum fraction
–t – Fourier conjugate
to transverse impact
parameter g
GPDs depend on 3 variables, e.g. H(x, x, t). They describe
the internal nucleon dynamics.

10. [ ] ò Link to DIS and Elastic Form Factors [ ] å ò ) ( , ~ q H D = ) ,
Form factors (sum rules) [ ) ( , ~
) Dirac f.f. 1 t G x E dx H F1 q P A = ] ò å -
) Pauli f.f. F2
DIS at x
=t=0 ) ( , ~ q H D = ) , ( ~ t x E H q [ ] ò - x +
- J G = = 1 ) , q( 2 E H
xdx
J q
X. Ji, Phy.Rev.Lett.78,610(1997)
Angular Momentum Sum Rule

11. Deeply Virtual Meson production
Universality of GPDs
Elastic form
factors
Real Compton
scattering at high t
Parton momentum
distributions
GPDs
Deeply Virtual Meson production
Deeply Virtual
Compton Scattering
Single Spin
Asymmetries

12. How can we determine the GPDs?

13. } Accessing GPDs in Exclusive Processes ep ® e ' p ' g ep e p L ® ' L
Deeply virtual Compton scattering (clean probe, flavor blind)
Sensitive to
all GPDs.
Insensitive to
quark flavor ep e ' p ' g ep e p L + - ' L
Hard exclusive meson production (quark flavor filter)
Sensitive to H, E ~ }
In a minute I’ll give an example of how GPDs show up in this processes.
4 GPDs in leading order, 2 flavors (u, d) → 8 measurements

14. Accessing GPDs through DVCS
Eo = 11 GeV
Eo = 6 GeV
Eo = 4 GeV BH
DVCS
DVCS BH p e
d4
dQ2dxBdtd
~ |TDVCS + TBH|2
TBH : given by elastic form factors F1, F2
TDVCS: determined by GPDs
I ~ (TBH)Im(TDVCS)
BH-DVCS interference generates beam and target polarization asymmetries that carry the proton structure information.

15. Measuring GPDs through polarization
s+ - s-
s+ + s- =
Polarized beam, unpolarized target: ~
H(x,t)
DsLU ~ sinfIm{F1H + x(F1+F2)H +kF2E}df
x = xB/(2-xB)
k = t/4M2
Kinematically suppressed
Unpolarized beam, longitudinal target: ~ ~
H(x,t)
DsUL ~ sinfIm{F1H+x(F1+F2)(H +x/(1+x)E) -.. }df
Kinematically suppressed
Unpolarized beam, transverse target:
H(x,t), E(x,t)
DsUT ~ sinfIm{k(F2H – F1E) + ….. }df
Kinematically suppressed

16. Pioneering Experiments Observe Interference
2001
e+p->e+pg
e-p->e-pg
AUL = asinf + bsin2f
First GPD analyses of HERA/CLAS/HERMES
data in LO/NLO consistent with a ~ 0.20.
A. Freund (2003), A. Belitsky et al. (2003)
twist-2
twist-3

17. Jefferson Lab - a DOE Science National Laboratory
JLab is a forefront facility with unique scientific and technical capabilities
One of 17 DOE National Laboratories
One of ten Office of Science National Laboratories
Serves an international user community of 1200
Experimental program to elucidate the
quark structure of matte delivers world leading
experiments in nuclear science
World leader and national resource in superconducting radiofrequency accelerating technology
Superconducting Radio Frequency (SRF) R&D yielded the new
single-crystal niobium cavity for use in future accelerators
Operates a high power Free Electron Laser
More than 1/3 of US Ph.Ds awarded in nuclear
physics; 248 Ph.Ds, granted, 192 more in progress
Excellent education program supporting local school science teaching

18. Jefferson Lab Today A C B Hall A Hall B Hall C Two high-resolution
4 GeV spectrometers
Large acceptance spectrometer electron/photon beams
Hall C
Be brief A B C
7 GeV spectrometer,
1.8 GeV spectrometer,
large installation experiments

19. Hall B – CLAS Present Day CLAS
Hall B currently houses the CEBAF Large Acceptance Spectrometer (CLAS) L=1034 cm-2s-1
Present Day
CLAS

20. Hall B - DVCS Solenoid and Calorimeter
Solenoid cryostat
Calorimeter

21. Deeply Virtual Compton Scattering & GPDs
Unprecedented set of Deeply Virtual Compton Scattering data accumulated in Hall A and with CLAS
Hall A
Phys.Rev.Lett.97:262002,2006
CLAS t
hard vertices g
A =
DsLU 2s
s+ - s-
s+ + s- =
At low and medium energies DVCS is the cleanest probe of GPDs. A hard virtual photon strikes a quark in the proton, which emits a hard real photon. The prpton remains intact and gets a transverse momentum kick. DVCS is sensitive to all 4 GPDs. Hall A cross section measurements showed that DVCS is consistent with dominance of the handbag mechanism. The CLAS data cover much larger kinematics in x_B, Q2, and t. but are currently limited to polarized beam asymmetries which also depend on the real parts of the Compton amplitude in a convolution integral that are more difficult to model. GPD based description show qualitative agreement with the CLAS asymmetry measurements. Nevertheless, these sets of data have been subjected to a model-independent extraction of the GPD related Compton form factors.
Polarized beam, unpolarized target:
Kinematically suppressed
DsLU ~ sinf{F1H + x(F1+F2)H +kF2E}df ~ Φ
Phys.Rev.Lett.100:162002,2008

22. In the past few years, we have made
a start in the quest to unravel the
Structure of the Proton.
What does the future hold?

23. JLab Upgrade to 12 GeV At 12 GeV, CEBAF will be an
ideal for GPD studies.
Add new hall
CHL-2
Enhance equipment in existing halls

24. Scope of the 12 GeV Upgrade

25. New Capabilities in Halls A, B, & C, and a New Hall D
9 GeV tagged polarized photons and a 4 hermetic detector D
Super High Momentum Spectrometer (SHMS) at high luminosity and forward angles C
High Resolution Spectrometer (HRS) Pair, and specialized large installation experiments A B
CLAS12 high luminosity, large acceptance.
A new Hall will be constructed to house the GlueX detector, that will conduct a search for excited mesons with gluonic components, and the existing Halls will be upgraded with new equipment as well. Hall C will have an additional super high momentum spectrometer. Hall A will retain the existing spectrometers and provide space for new specialized equipment to address a variety of physics topics. Hall B will house the CLAS12 detector which is the focus of this of workshop. At 12 GeV JLab will be ideal for precision studies at large Bjorken x.

26. Hall B 12GeV upgrade overview
Hall B currently houses the CEBAF Large Acceptance Spectrometer (CLAS) L=1034 cm-2s-1
CLAS will be replaced by CLAS12
CLAS12 is designed to operate with an upgraded luminosity of
L=1035 cm-2s-1
CLAS12 will be world wide the only large acceptance high luminosity spectrometer for fixed target electron scattering experiments
CLAS12
Present Day
CLAS

27. CLAS12 – Design parameters
Forward Detector
Forward Central
Detector Detector
Angular range
Tracks 50 – – 1250
Photons 30 – n.a.
Resolution
dp/p (%) < 5 GeV/c < 1.5 GeV/c
dq (mr) < 1 <
Df (mr) < 3 < 5
Photon detection
Energy (MeV) >150 n.a.
dq (mr) 1 GeV n.a.
Neutron detection
efficiency < 0.7 (EC+PCAL) n.a.
Particle ID
e/p Full range n.a.
p/p Full range < 1.25 GeV/c
p/K Full range < 0.65 GeV/c
K/p < 4 GeV/c < 1.0 GeV/c
p0gg Full range n.a.
hgg Full range n.a.
Central Detector

28. Central Detector Forward Detector
FTOF 2
LTCC
FTOF 1a
FTOF 1b
PCAL
DC R1, R2, R3
Central
Detector
Solenoid
SVT EC
CTOF
Forward
Detector
TORUS
HTCC

29. CLAS12 Central Detector
Superconducting 5T Solenoid Magnet, 78cm ø warm bore.
Central Time-of-Flight array (CTOF)
Silicon Vertex Tracker
Extension under development
Tracking w/ Micromegas
Neutron Detector

30. CLAS12 – Central Detector SVT, CTOF
SVT - Charged particle tracking in 5T field
Vertex reconstruction
ΔT < 60psec in CTOF for particle id
Moller electron shield
Polarized target operation ΔB/B < 10-4
in 3x5 cm cylinder around center
CTOF 6
layers
8 layers
SVT

31. CLAS12 – Solenoid and Torus Magnets
The Torus and Solenoid magnets provide bending power for tracking with sufficient momentum resolution to allow exclusive processes to be identified. At forward angles the Torus field provides large integral Bdl while the solenoid provides tracking at large angles over a limited radial distance.
The B-field transverse to the particle trajectory is approximately matched to the average particle momentum.

32. A Program at the Forefront of Hadron Physics
3D Structure of the Nucleon Structure - the new Frontier in Hadron Physics
Nucleon GPDs and TMDs – exclusive and semi-inclusive processes with high precision
Precision measurements of structure functions and forward parton distributions at high xB
Elastic & Transition Form Factors at high momentum transfer
Hadron Spectroscopy – heavy baryons, hybrid mesons
Some of the topics to be addressed are – the 3D structure of the nucleon which is a new frontier of hadron physics. This requires measurements of GPDs and TMDs in deeply exclusive and semi-inclusive processes.

33. Initial Science Program
CLAS12
Physics Focus
Approved experiments
LOIs
supported
GPD’s & exclusive Processes 3 1
TMDs & SIDIS 4
Parton Distribution Function & DIS 2
Elastic & resonance form factors
Hadronization & Color Transparency
Baryon Spectroscopy
Total 13 7
Approved experiments correspond to about 5 years of scheduled beam operation .

34. CLAS12 Institutions Institution Focus Area
Argonne National Laboratory (US) Cerenkov Counter
California State University (US) Cerenkov Counters
Catholic University of America (US) Software
College of William & Mary (US) Calorimetry, Magnet Mapping
Edinburgh University (UK) Software
Fairfield University (US) Polarized Target
Florida International University, Miami (US) Beamline/Moller polarimeter
Glasgow University (UK) Central Detector, DAQ, Forward Tagger, RICH
Grenoble University/IN2P3 (France) Central Detector
Idaho State University (US) Drift chambers
INFN –University Bari (Italy) tbd, interest in RICH
INFN –University Catania (Italy) tbd
INFN – Frascati and Fermi Center (Italy) Central Neutron Detector+ interest show in RICH
INFN –University Ferrara (Italy) (will join in 2010) tbd, interest in RICH
INFN – University Genoa (Italy) Central Neutron Detector+ interest in Forward Tagger
INFN – ISS/Rome 1 (Italy) tbd, interest in RICH
INFN – University of Rome Tor Vergata (Italy) Central Neutron Detector+ HD target
Institute of Theoretical and Experimental Physics (Russia) SC. Magnets, Simulations
James Madison University (US) Calorimetry
Kyungpook National University (Republic of Korea) CD TOF
Los Alamos National Laboratory (US) Silicon Tracker
Moscow State University, Skobeltsin Institute for Nuclear Physics (Russia) Software, SVT
Moscow State University (High Energy Physics) (Russia) Silicon Tracker
Norfolk State University (US) Preshower Calorimeter
Ohio University (US) Preshower Calorimeter
Orsay University/IN2P3 (France) Central Neutron Detector
Old Dominion University (US) Drift Chambers
Renselear Polytechnic Institute (US) Cerenkov Counters
CEA Saclay (France) Central Tracker, Reconstruction software
Temple University, Philadelphia (US) Cerenkov Counters
Thomas Jefferson National Accelerator Facility (US) Project coordination & oversight
University of Connecticut (US) Cerenkov Counters
University of New Hampshire (US) Central Tracker, Offline Software
University of Richmond (US) Offline Software
University of South Carolina (US) Forward TOF
University of Virginia (US) Beamline/Polarized Targets
Yerevan Physics Institute (Armenia) Calorimetry

35. Deeply Virtual Exclusive Processes - Kinematics Coverage
of the 12 GeV Upgrade
H1, ZEUS
H1, ZEUS
11 GeV
27 GeV
200 GeV
11 GeV
JLab Upgrade
12 GeV
COMPASS
W = 2 GeV
HERMES
Study of high xB domain
requires high luminosity
0.7

36. DVCS/BH- Beam Asymmetry
Ee = 11 GeV
ALU
With large acceptance,
measure large Q2, xB, t
ranges simultaneously.
A(Q2,xB,t)
Ds(Q2,xB,t)
s (Q2,xB,t)

37. CLAS12 - DVCS/BH- Beam Asymmetry
Ee = 11 GeV
Q2=5.5GeV2
xB = 0.35
-t = 0.25 GeV2
Luminosity = 720fb-1

38. CLAS12 - DVCS/BH Beam Asymmetry
e p epg
E = 11 GeV
DsLU~sinfIm{F1H+..}df
Selected
Kinematics
L = 1x1035
T = 2000 hrs
DQ2 = 1 GeV2
Dx = 0.05

39. CLAS12 - DVCS/BH Target Asymmetry
E = 11 GeV
L = 2x1035 cm-2s-1
T = 1000 hrs
DQ2 = 1GeV2
Dx = 0.05
e p epg
Longitudinally polarized
target ~
Ds~sinfIm{F1H+x(F1+F2)H...}df

40. CLAS12 - DVCS/BH Target Asymmetry
Sample kinematics
e p epg
E = 11 GeV
Q2=2.2 GeV2, xB = 0.25, -t = 0.5GeV2
Transverse polarized target
Ds ~ sinfIm{k1(F2H – F1E) +…}df
AUTx Target polarization in the
scattering plane
AUTy Target polarization perpendicular
to the scattering plane
Asymmetries highly sensitive to the u-quark contributions to the proton spin.

41. Exclusive r0 production on transverse target
2D (Im(AB*)) T
AUT ~
A ~ 2Hu + Hd r0
Q2=5 GeV2
B ~ 2Eu + Ed
A ~ Hu - Hd
B ~ Eu - Ed r+ r0
Eu, Ed allow to map the
orbital motion of quarks. B
K. Goeke, M.V. Polyakov, M. Vanderhaeghen, 2001

42. ∫ Tomographic Images of the Proton Ed(x,t) Eu(x,t) d2t (2p)2
Target polarization
dX(x,b ) T
Ed(x,t)
Eu(x,t)
uX(x,b ) T ∫
d2t
(2p)2
e-i·t·b E(x,0,t) T
q(x,b ) =
flavor
polarization
CAT scan slice
of human abdomen
M. Burkardt

43. 2007 NSAC Long Range Plan (4 recommendations)
We recommend the completion of the 12 GeV Upgrade at Jefferson Lab.
- It will enable three-dimensional imaging of the nucleon, revealing hidden aspects of its internal dynamics.
It will complete our understanding of the transition between the hadronic and quark/gluon descriptions of nuclei.
It will test definitively the existence of exotic hadrons, long-predicted by QCD as arising from quark confinement.
It will provide low-energy probes of physics beyond the Standard Model complementing anticipated measurements at the highest accessible energy scales.
The importance of GPDs for the future of hadronic and nuclear physics was recognized last week by the NSAC Long Range Plan meeting in Galveston. The board gave the Jlab upgrade the highest recommendation and lists the 3-D imaging of the nucleon as the #1 program for the upgrade.

44. DOE Generic Project Timeline
We are here
Almost half-way between CD1 and CD2
MAR 2004
FEB 2006
NOV 2007
SEP 2008
12 GeV Upgrade – Approval dates

45. DOE Project Critical Decisions – 12 GeV Schedule
CD-0 Approve Mission Need (Mar 2004)
CD-1 Approve Alternative Selection and Cost Range (Feb 2006)
Permission to develop a Conceptual Design Report
Defines a range of cost, scope, and schedule options
CD-2 Approve Performance Baseline (Nov 2007)
Fixes “baseline” for scope, cost, and schedule
Now develop design to 100%
Begin monthly Earned Value progress reporting to DOE
Permission for DOE-NP to request construction funds
CD-3 Approve Start of Construction
DOE Office of Science CD-3 Approval: September 15, 2008
CD-4 Approve Start of Operations or Project Close-out

46. 12 GeV Upgrade – Immediate Future
12 GeV Upgrade Project Start of Construction: October 2008

47. 12 GeV Schedule
May ’11 - Oct ‘ month “down” for initial installations
Nov ’11 - May ‘ month run 6GeV
Jun ’12 - May ‘13: 1-year “down” for major installation
June ’13 - Sep ‘13: Accelerator commissioning

48. 12 GeV Schedule Oct ‘13: Hall A commissioning start
Apr ‘14: Hall D commissioning start
Oct ‘14: Hall B & C commissioning start

49. Summary
The JLab Upgrade has well defined physics goals of fundamental importance for the future of hadron physics, addressing in new and revolutionary ways the quark and gluon structure of hadrons by
accessing GPDs and TMDs
mapping the valence quark structure of nucleons with high precision
understanding hadronization processes
extending nucleon form factors to short distances
Design of accelerator and equipment upgrades are underway
Construction started October 2008

50. 12 GeV Upgrade Science, Technology & Education
Jefferson Laboratory
12 GeV Upgrade Science, Technology & Education
Center Stage

51. This is a very exciting time for hadronic physics, and the perfect time for new collaborators to make significant contributions to the physics and equipment of CLAS12